Development and Experimental Validation of End-Fire Synthetic Aperture Sonar for Sediment Scattering Studies

Shannon-Morgan Steele
Master's Thesis Defense


Friday, Mar. 8, 2019, 1:00pm
Chase 130

Seafloor sediment acoustic returns are comprised of scattering from both the sediment-water interface and the sediment volume. At low-frequencies, volume scattering is often the dominant mechanism; however, direct measurements of this component have rarely been made, owing to the large beamwidths typically associated with low-frequencies. When beamwidths are large, the sediment interface and volume returns arrive at the same time, causing estimates of volume scattering to become biased by the interface scattering. End-Fire Synthetic Aperture Sonar (EF-SAS) can achieve narrower beamwidths by coherently combining multiple acoustic returns as a vertically oriented transmitter and/or receiver is moved towards the seafloor. A beampattern model developed for EF-SAS suggests EF-SAS processing can reduce the beamwidth of a sonar by a factor of 5 with an array length of 100 wavelengths. In this thesis, EF-SAS processing methods will be developed and the resulting gains will be experimentally verified through a motion-controlled EF-SAS field trial. Experimental tests indicate that EF-SAS gains can be accurately predicted using the EF-SAS beampattern model. Analysis of the data demonstrates the ability of EF-SAS to reduce interface scattering. We will demonstrate how EF-SAS can produce a variety of data products relevant to seafloor characterization, including: the angular response of interface and volume scattering, the sediment reflection coefficient, and the sediment attenuation coefficient. This thesis will conclude with recommendations for the development of a specialized EF-SAS tool, and an analysis of its applications.


In 2016, Shannon completed her undergraduate degree at Dalhousie University with first class honours in Earth Sciences and Oceanography, and a certificate in Environmental Geoscience. Shannon’s honours thesis on seafloor scattering and reverberation with Defence Research Development Canada solidified her passion for Acoustical Oceanography and its applications to mapping the seafloor and subsurface. Shannon spent the summer before joining CCOM at Dalhousie University modeling sound propagation from tidal turbines and is excited to get back to studying the seafloor and subsurface. Shannon is pursuing a Master’s in Oceanography with a focus on bottom interacting acoustics.